Aaand, if my EmojiInput extension for Chrome is any indication of how they'd look on Android devices, they're way too small in comparison with the middle (like, the icons we have now are closer to the right size than that). Not to mention, they're entirely the wrong color.

I agree with having a difference between something planned, but not playable, and a released part of a case. Somebody browsing the forums for something to play (but not necessarily complete) would want to avoid the former, but not the latter.The only Unicode symbols I could find that fit ○ and ● (which I'd like to keep since they work nicely) are ◌ and ◙. The former is kind of hard to distinguish from ○, though, at least on my machine, so the latter is probably the best choice.

Yes. The other symbols have been around so long, I see no reason to change them if we don't have to (the only reason I suggested changing the original was the size difference, but since the diamond is pretty close in size, that's no longer an issue).